This invention relates to anti-fouling materials for inhibiting marine growth on submerged articles, particularly boat hulls. Specifically, this invention utilizes a plastic anti-fouling film for controlling the growth of algae, barnacles, mussels, fungi and other marine organisms on a boat hull in salt and/or fresh water.
The growth of algae, fungi, barnacles, mussels and other marine organisms on submerged structures, such as boat hulls, is referred to as marine xe2x80x9cfoulingxe2x80x9d and results in rough, biologically encrusted surfaces. Marine fouling of boat hulls causes many problems such as fuel waste, difficulty of boat steering and maneuvering due to increased drag, as well as damage to the boat hull itself. The rougher the hull, the more fuel the boat requires to maintain its speed through water. It is estimated that fuel savings alone could amount to several hundred million dollars annually through the use of anti-fouling techniques.
The rapid growth of marine organisms on underwater surfaces has long been a problem in the marine industry. Various chemically treated anti-fouling paints have traditionally been used to combat this kind of unwanted growth However, many of the chemicals incorporated with anti-fouling paints have been found to be toxic to non-target organisms, thereby mandating severe restrictions as to the use and application of such chemicals.
Anti-fouling paints have a myriad of problems associated with their use. For example, as anti-fouling paint ages, toxic chemicals leach out of the paint and the paint subsequently becomes a less effective deterrent to marine growth and must be replaced. Anti-fouling paint coatings are typically about 1.5 mm thick and thus need to be replaced annually in harsh salt water environments such as those around Florida and California. Before the old anti-fouling paint can be sanded or scraped off the hull, however, it is often necessary to scrape off the plentiful growth of barnacles, mussels, and any other marine organisms which have accumulated due to the decreased effectiveness of the paint over time. The removal of these organisms is quite time consuming and extremely laborious due to these organism""s great adhesive strength. The boat hull must then be repainted with a fresh coat of anti-fouling paint.
A major drawback of this tedious work is that these anti-fouling paints contain ingredients that are highly toxic not only to barnacles and other marine growth, but also to the individuals applying the paint and subsequently removing it years later. The effect of paint dust or particles on the worker""s health has thus become an important issue and a major concern associated with anti-fouling paints.
Anti-fouling paints also pose environmental hazards. Overspray during application, water run-off occurring during paint removal, and disposal of paint waste must be closely monitored and controlled to avoid long term environmental and ground water pollution.
Another disadvantage is that these anti-fouling paints are extremely expensive due to special precautions that need to be taken in their application, removal and disposal. In Florida, for instance, individuals must drape plastic tarps under and around a boat hull to catch the ground-off paint dust, new paint overspray and drippings. These tarps must then be bagged and specially marked as hazardous materials and shipped off site to a proper, pre-approved disposal location. Due to such special handling, extra shipping precautions and added disposal requirements, these anti-fouling paints are expensive to utilize.
A common anti-foulant ingredient utilized in these paints is copper and copper based compounds. The major disadvantage of copper based paint is that it can cause galvanic corrosion of aluminum vessels. Even with high quality anti-corrosive primers, flaws in the primer coat may result in corrosion of an aluminum hull, especially those with extended periods between dry dockings. Therefore, copper based anti-foulant paints are impractical for aluminum boats.
Another anti-fouling compound is tributyltin (TBT). Currently, owners of aluminum based boats use tributyltin based paints to inhibit marine fouling. A common TBT compound utilized is tributyltin methacrylate. Although use of TBT avoids the corrosive effects of copper on aluminum, paints utilizing TBT still retain all of the disadvantages of anti-fouling paint previously mentioned.
Due to the problems associated with anti-fouling paints, other anti-fouling techniques have been utilized, albeit with very limited success. For example, another anti-fouling method used is to xe2x80x9cplantxe2x80x9d a multiplicity of filaments on the surface of the boat hull or marine structure. The filaments flutter in the seawater so as to effectively prevent marine growth. However, it has been found that filaments which are fine enough to ensure sufficient fluttering to inhibit marine growth tend to get deformed, damaged, and entangled with one another in a short period. This results in the impairment of the fluttering characteristic, which in turn reduces the anti-fouling effect of the filaments.
The present invention provides an anti-fouling protective layer for preventing attachment of marine organisms to an underwater surface. More specifically, the anti-fouling protective layer comprises a plastic film having inner and outer surfaces, and a thermoplastic adhesive disposed between a structure intended to be submerged underwater and the inner surface of the film, said adhesive being of the type that upon heating removably adheres the film to the underwater surface of said structure. Either the plastic film or the thermoplastic adhesive is impregnated with an anti-fouling compound so that when attached to said structure, the anti-fouling compound prevents growth of marine organisms on the plastic film.
In one form, the plastic film is impregnated with an anti-fouling compound so as to prevent marine organisms from attaching to the plastic film. A hygroscopic plastic film may best allow a slow release of the anti-fouling compound into the surrounding aqueous environment and thus prevent the growth of marine organisms on the film.
In another embodiment, the thermoplastic adhesive is impregnated with the anti-fouling compound. In this embodiment, the outer plastic film must be permeable to allow release of the anti-fouling compound and prevent the growth of marine organisms on the outer plastic film.
Preferably, the outer plastic film includes a plurality of minute openings formed therethrough to allow the slow release of said anti-fouling compounds.
In yet another embodiment, an insulating film is disposed between the substrate containing the anti-fouling compound and the underwater surface. The insulating film is used to provide a barrier to prevent corrosion of the submerged structure by the anti-fouling compound. This embodiment would typically be utilized if a copper based anti-foulant ingredient was utilized on an aluminum boat hull. Preferably, the insulating film would be coextruded with the plastic film which is impregnated with the anti-fouling compound so as to be located between the plastic film and the adhesive. Alternately, the insulating film could be located between the adhesive layer and the surface to be protected if the adhesive layer is the substrate impregnated with the anti-fouling compound.
Preferably, the anti-fouling film has the heat sensitive thermoplastic adhesive pre-applied to its inner surface for ease of handling, but the film and adhesive may be separate components if desired. The film may be applied to a structure such as a boat hull by stretching the film over the hull and preferably taping it in place. Utilizing a heat gun and roller, the film and adhesive is heated, rolled onto the hull surface, and then allowed to cool. The anti-fouling film is thus adhesively bonded to the hull and will remain bonded until later removed. To replace old film, the film and adhesive is re-heated to soften the adhesive. The film is then stripped from the hull along with any barnacles, mussels and other marine growth which may be attached to the film. This eliminates the need for scraping organisms off the hull since they are simply removed when peeling off the film. This invention thus reduces the time and effort associated with removing marine growth directly from the boat hull. The invention also advantageously leaves no dust, overspray or toxic particles in the environment upon removal of the film. The used film may be placed in a plastic bag after removal for proper disposal or can be sent to a manufacturer for re-fabricating or recycling. A new plastic anti-fouling film can then be applied.
In still another embodiment, a laminate comprising a plastic film and a first adhesive impregnated with the anti-fouling compound is applied to the underwater surface of the structure. However, in this embodiment, the plastic film is peeled off of the first adhesive after application to the structure, leaving only the first adhesive containing the anti-fouling compound in direct contact with the outside environment. The first adhesive is removed after the anti-fouling agent has lost effectiveness by applying a removing laminate comprised of a carrier film and a second adhesive over the first adhesive, heating the carrier film and first and second adhesives to soften and bond the first adhesive to the second adhesive, and peeling off the carrier film together with the first adhesive now bonded to the second adhesive.